Magnetic Susceptibility Change Mechanism In Kurtak,Siberia And Its Paleoclimate Significances

The loess-paleosol succession of Kurtak, along the western slope of the Yenisei Valley, is one of the best documented Middle Pleistocene sequences in southern Central Siberia. About the Kurtak loess-paleosol, the magnetic susceptibility of loess is higher than the paleosol. Many researchers believed the reason of that is "Alaska mode", in which the fluctuation of wind during glacial-interglacial period gives rise to the higher magnetic susceptibility of loess. Some evidences proved that the magnetic susceptibility of paleosol will decrease after pedogenic process. However, there is no explanation to quantify the extent of fluctuation of wind and pedogenic process well. The studies that employ magnetic parameters such as magnetic susceptibility to reconstruct the paleoclimate quantitatively or semi-quantitatively belong to the pre-area of the subject, but the key point is that we need to make clear the changing mechanism of magnetic susceptibility of deposits. Therefore, in order to explore the changing mechanism of magnetic susceptibility of deposits under wet cold condition in middle and high latitudes, we analyze the magnetic and grain-size parameters of samples from Kurtak Profile. We also reconstruct the paleoclimate by analyzing these parameters. The primary conclusions of the research are as follows:About Kurtak Profile, SoO soil had developed during Holocene. The magnetic susceptibility of SoO soil is similar to loess on the whole. The gap of magnetic susceptibility between sediments transported by wind during glacial and interglacial period is smaller than the gap between loess and paleosol. When heated, the amplification factor of the magnetic susceptibility of paleosol is larger than that of loess, which indicates that the magnetism of paleosol reduced drastically after the process of pedogenesis. Compared with the fluctuation of wind, the main cause of the drop in magnetic is the pedogenic process.Along with the strata, the cyclical fluctuation of magnetic and grain-size parameters in-phase is corresponding to the warming and cooling trends in Siberia since the Middle Pleistocene. The variation trend of the two parameters is in accord with the change of magnetic susceptibility of Xi Feng Profile which is located on China Loess Plateau. It's also in agreement with the trend of the marine oxygen isotope (MIS) curves from tropical Indian Ocean. We conclude that it is synchronous in climate change among East Asia, from low latitude to high latitude since 280 ka.